1. Field of the Invention
The present invention relates to a coil bobbin, and more particularly to an improvement on a configuration of a leader cable accommodating groove portion of a coil bobbin.
2. Description of the Prior Art
An example of a conventional coil bobbin is illustrated in FIGS. 13, 14 and 15. The coil bobbin of this type comprises a main cylinder portion 1 opened at both ends thereof and made of a thin-walled resin around which a coil is wound, and a leader cable accommodating groove portion 2 for accommodating a leader cable. The leader cable accommodating groove portion 2 is made of a thin-walled resin, and disposed in a manner surrounding the main cylinder portion 1 at one end of the main cylinder portion 1 on an outer peripheral surface of the main cylinder portion 1. An outer peripheral configuration of the main cylinder portion 1 can be formed in various shapes, for instance, in a square cylinder, a simple cylinder or the like. The leader cable accommodating groove portion 2 has a shape which agrees with an outer periphery of the main cylinder portion 1.
An example of the conventional leader cable accommodating groove portion 2 is illustrated in FIGS. 13, 14 and 15. This leader cable accommodating groove portion 2 includes a bottom plate portion 21 disposed at one end of the main cylinder portion 1 in manner projecting from an entire periphery of the main cylinder portion 1 outward in a radial direction, a side wall portion 22 extending from a front end of the bottom plate portion 21, disposed away from the main cylinder portion 1 by a predetermined distance and extending in an axial direction, and a groove opening 23 opened in an axial direction.
At predetermined positions of the side wall portion 22, take-out cut-offs "d1" and "d2" are disposed in order to take out coiled cables "L1" and "L2." Further, as illustrated in FIG. 15, at another position of the side wall portion 22, a take-in cut-off "d4" is disposed in order to take leader cables "L3" and "L4" in. Furthermore, at the position of the take-in cut-off "d4," a leader cable holding plate portion 3 is disposed in a manner projecting from an outer periphery of the bottom plate portion 21 outward in a radial direction. Moreover, as illustrated in FIGS. 13 and 14, on both sides of the leader cable holding plate portion 3, presser covers 31 and 32 of a letter "L" shape substantially are disposed, thereby pressing and holding leader cables "L3" and "L4." As also illustrated in FIG. 14, the leader cables "L3" and "L4" are thus accommodated in the leader cable accommodating groove portion 2.
The leader cables "L3" and "L4" are inserted into the leader cable accommodating groove portion 2 as follows. First, the leader cables "L3" and "L4" are inserted into the leader cable holding plate portion 3. Thereafter, the leader cables "L3" and "L4" are pressed in an axial direction into the leader cable accommodating groove portion 2 by way of the groove opening 23 (See FIG. 15.).
Another example of the conventional leader cable accommodating groove portion 2 is illustrated in FIGS. 16, 17 and 18. This leader cable accommodating groove portion 2 includes a side wall portion 22, which is formed by cutting off the side wall portion 22 of the above-described conventional leader cable accommodating groove portion 2 by a semicircle on a side of the leader cable holding plate portion 3, and retainer plates 4 of a triangular shape substantially. The retainer plates 4 are disposed at two (2) predetermined positions on an outer periphery of the main cylinder portion 1, and they are provided in order to compensate the cut-off side wall portion 22. The leader cables "L3" and "L4" has been thus inhibited from coming off the leader cable accommodating groove portion 2 outward in an axial direction.
The leader cables "L3" and "L4" are inserted into the leader cable accommodating groove portion 2 as follows. First, the leader cables "L3" and "L4" are inserted into the leader cable holding plate portion 3. Thereafter, the leader cables "L3" and "L4" are bent inward in a radial direction, and then inserted into a space (See FIG. 18.) between the retainer plates 4 and the bottom plate portion 21. Finally, the leader cables "L3" and "L4" are pressed in an axial direction into the leader cable accommodating groove portion 2 by way of the groove opening 23.
It is apparent from the above-described two (2) examples of the conventional coil bobbin that the important thing in the manufacture of the coil bobbin is how to hold the leader cables "L3" and "L4" connected to the coiled cables "L1" and "L2" stably in the leader cable accommodating groove portion 2. When the leader cables "L3" and "L4" are displaced by external force, shock, vibration or the like, the leader cables "L3" and "L4" come off the leader cable accommodating groove portion 2, or the coiled cables "L1" and "L2" connected to the leader cables "L3" and "L4" break up. Here, there are two (2) vibrations, i.e., a vibration due to external cause and a self-vibration due to self-generating electromagnetic force.
For instance, in the case of the conventional leader cable accommodating groove portion 2 illustrated in FIG. 13, the leader cables "l3" and "L4" are stably held at an inlet portion of the leader cable accommodating groove portion 2 and they are inhibited from moving in a radial direction by the leader cable accommodating groove portion 2. However, the leader cables "L3" and "L4" can move to the side of the groove opening 23, namely outward in an axial direction, in the leader cable accommodating groove portion 2. When the leader cables "L3" and "L4" are left to move in such a manner, there is a fear for breaking up the coiled cables "L1" and "L2."
Further, after the leader cables "L3" and "L4" are accommodated in the leader cable accommodating groove portion 2 as illustrated in FIG. 14, a whole of the coil bobbin is molded together with the coils by using a resin in the conventional coil bobbin for a certain application. In such a coil bobbin, the leader cables "L3" and "L4" come off the leader cable accommodating groove portion 2 when placing the coil bobbin in a mold. Accordingly, there occurs failure molding.
In order to solve the problems described so far, the leader cables "L3" and "L4" are adhered onto the bottom plate portion 21 for a certain application. However, such an increase in the number of the manufacturing processes results in disadvantage in view of the strict cost reduction requirement imposed on the coil bobbin.
On the other hand, in the case of the other conventional leader cable accommodating groove portion 2 illustrated in FIG. 16, the leader cables "L3" and "L4" are held stably at the inlet portion of the leader cable accommodating groove portion 2. In the leader cable accommodating groove portion 2, the halves of the leader cables "L3" and "L4" on the side of the leader cable holding plate portion 3 are inhibited from coming off outward in an axial direction by the retainer plates 4, and the other halves of the leader cables "L3" and "L4" on the front end sides are inhibited from coming off outward in a radial direction by the side wall portion 22. As a result, the leader cables "L3" and "L4" holdability of the other leader cable accommodating groove portion 2 illustrated in FIG. 16 is improved with respect to the one illustrated in FIG. 13.
However, the operation of connecting the leader cables "L3" and "L4" with the coiled cables "L1" and "L2" with the coiled cables "L1" and "L2" is usually carried out on an outside of the leader cable accommodating groove portion 2 in a radial direction, for instance, the connecting operation is carried out as illustrated in FIG. 3. After completing the connecting operation, the front ends of the leader cables "L3" and "L4" should be bent inward in a radial direction and accommodated in the leader cable accommodating groove portion 2. Accordingly, the bent front ends of the leader cables "L3" and "L4" tend to bend back outward in a radial direction because of their elasticity. Since the side wall portion 22 should be disposed at portions of the leader cable accommodating groove portion 2 for accommodating the front ends of the leader cables "L3" and "L4" and since no retainer plate 4 cannot be disposed at the portions, the leader cables "L3" and "L4" are still liable to come off outward in an axial direction. Thus, the front ends of the leader cables "L3" and "L4" can hardly enjoy the effect of the provision of the retainer plates 4.